The poll's release comes a day after a new NBC News-Marist poll showed Pryor leading Cotton by double digits. The survey found Pryor ahead of Cotton, 51 percent to 40 percent. That poll was the third survey since April 1 to show Pryor with a double digit lead over Cotton.

The Cotton campaign poll, published by Roll Call on Tuesday, shows Cotton leading Pryor 42 percent to 40 percent.

In the memo accompanying the internal poll, pollster Wes Anderson said the NBC-Marist poll under-sampled Republicans. Anderson also criticized the survey for polling registered voters rather than likely voters.

The internal Cotton campaign poll was conducted by OnMessage Inc. It surveyed 600 likely voters across Arkansas between May 6 and May 8. Thirty-six percent of those surveyed were Republicans, 36 percent were Democrats, and 26 percent were Independents. The poll had a margin of error of plus or minus 4 percentage points.